This invention relates to indicators of the type wherein the application of a force to a member causes a visual change to take place in an indicator element.
In many assembly operations where fastening devices are used it is desirable to inspect the assembled fastener to determine that it has been taken up an appropriate amount. The fastener may be, for example, a stud, a bolt, a rivet or the like.
Several prior art techniques have been utilized for determining when a fastener has been properly taken up. One such technique involves the use of a torque wrench in which a specified number of foot-pounds may be verified as having been applied to the fastener in the assembly thereof. Other prior art techniques have made use of the fact that take-up of a fastener will set up certain stress levels in the fastener which may be measured as, for example, by means of a stress sensitive material. Still further prior art techniques have made use of the fact that take-up of a fastener produces an elongation of the fastener which may be measured utilizing well known techniques such as direct measuring devices.
In U.S. Pat. Nos. 3,602,186 and 3,799,108 there are shown and described indicators of the type wherein the displacement of an indicator area within fluid produces a visual change in appearance of the indicator area as viewed through a translucent window. In U.S. Pat. No. 3,908,508 there is shown and described a non-fluid indicator of the type wherein the application of stress to a member causes movement within an indicator assembly. There is thus presented a change in optical appearance of the indicator assembly which is a function of the degree of tension applied to a strain member.
This invention is directed to an all mechanical or non-fluid type indicator which includes an indicator element. The indicator element is deformable as a function of the application of a force to a strain member. As a consequence there is produced a visual indication of the degree of loading (or the absence thereof) applied to a strain member.